A crucial need exists for effective and cost-efficient obesity management in primary care. Obesity is prevalent, causally or therapeutically important in many serious chronic conditions, and accounts for at least 5 percent of all health care expenditures in the US. Interventions to control the obesity epidemic must produce long term changes in diet and exercise behaviors and be effectively applied in primary care settings. Previous attempts to control obesity acutely with unrealistic diets, surgery, medications or intensive counseling programs cannot be applied to large numbers of patients because they are expensive, and do not produce lasting results. Our intervention (TM-CD) is based on the proposition that obesity is a chronic disease (CD) which can be managed by changing six behaviors necessary for weight loss--increased exercise, increased usual activity, portion control, decreased dietary fat, increased fruit consumption, and increased vegetable consumption. The TM-CD intervention recognizes that obese patients may be in different stages of change for each behavior and applies principles of the Transtheoretical Model (TM) to help patients move toward action and maintenance for six behaviors necessary for weight loss. Patients in the TM-CD intervention group will be profiled for stage of change for the six target behaviors and then receive:stage and behavior matched educational handouts to encourage action for the behaviors, monthly stage-matched telephone callbacks from a weight-loss advisor, repeat stage of change profiling every two months, and biannual consultation with a dietitian linked with an assessment of key trial outcomes. Primary care physicians will receive formal training to enhance behavior change using periodic feedback about TM-CD patients' psychological, behavioral, and biological status. Patients in the traditional care (control) group will be exposed to periodic dietary and exercise evaluations, limited standard advice from a dietitian, and usual physician care. We propose a 24 month, multi-center, randomized control trial of 540 primary care patients comparing the TM-CD intervention to traditional care. We hypothesize that compared to traditional care patients, TM-CD patients will show greater improvements in key trial outcomes (energy consumption and expenditure, weight, body mass index, waist/hip ratio, and lipids). The TM-CD intervention is unique in its application of the principles of the TM Model of change in combination with the tenets of the chronic disease care paradigm in primary care.